A chlorine atom is a single, neutral atom of the element chlorine (Cl). It has 17 protons and 17 electrons, and is the lightest halogen. Chlorine atoms are highly reactive and do not exist as individual atoms in nature.

A chlorine ion is a chlorine atom that has lost one electron, resulting in a net negative charge. It has 17 protons and 16 electrons. Chloride ions are stable and commonly found in nature, such as in seawater and rock salt.